The present invention relates to a screw compressor, particularly to a screw compressor with a simple construction suitable for efficiently separating oil from discharge gas.
In a conventional screw compressor, as disclosed in Japanese Patent Unexamined Publication No. 10283/1993, a mesh demister is provided in a discharge chamber such that the former includes the whole of a cross section of the latter. There is such a structure that discharge gas discharged from a discharge casing into the chamber is passed through the mesh demister to separate oil contained in the discharged gas.
The efficiency of such a mesh demister separating oil is connected with the speed of gas passing. Either of the speed and flow rate of gas discharged into the discharge chamber has a distribution in a cross section of the chamber. So the gas passes through the mesh demister at uneven speeds and flow rates. More specifically, either of the speed and flow rate near the outlet of a discharge passage of the discharge casing is greater than that of the other parts.
That is, in the whole of the mesh demister, the flow rate in the downstream part of the discharge outlet is great but the speed therein is far from the optimum passing speed for the mesh demister. This causes a problem of remarkably reducing the oil separation efficiency. For solving this problem, some measures were hitherto conventionally taken, e.g., an obstacle plate is provided independently in the chamber or modifying flow passage of discharge gas to change the direction of gas flow and thereby make the flow rate distribution in the chamber even.
However, those measures also have such problems as that the fixing portion of the independent obstacle plate is apt to be damaged, oil scatters again immediately after colliding, and the performance of the compressor deteriorates with an increase in pressure loss due to change of the flow direction.